Spatial structure in the zooplankton of a newly formed and heavily disturbed urban lake

Abstract

Physico-chemical gradients and local biotic interactions combine at different scales to cause spatial heterogeneity among lake zooplankton. However, current understanding is based overwhelmingly on natural systems and there have been few assessments of zooplankton spatial pattern in artificial lakes subjected to intensive management. Here, we investigate spatial structure among crustacean zooplankton at scales ranging from 1 m to 2700 m in the newly-formed Cardiff Bay (UK). We hypothesised that zooplankton spatial structuring in Cardiff Bay would be weakened by artificial aeration that was expected to create intense, continuous disturbance that homogenised physico-chemical conditions. Water quality across Cardiff Bay varied only moderately, and variations in zooplankton community composition were weakly related to temperature, oxygen, chlorophyll-a concentration and salinity at scales of around 2 km. However, spatial pattern explained over 60 % of variance in zooplankton composition at the smallest scales (0-5 m), implying that inter-specific interactions were involved. Additionally, the numerically dominant zooplankton (Daphnia hyalina (Leydig 1860), Eurytemora affinis (Poppe 1880) and Eucyclops agilis (Koch 1838)) had highly contagious distributions in warmer locations with increased chlorophyll-a reflecting aggregated response to abundant food. These data suggest that local biotic interactions among zooplankton and broader-scale links between dominant species and their algal food are sufficiently intense to persist despite the homogenising effects of artificial aeration and lake mixing. Such spatial pattern and scale-dependence has ramifications for zooplankton sampling while illustrating the self-organising capacity of predator-prey interactions even in novel, disturbed environments.